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Standards of Care April 2006 (Vol 8, No 3)

Ferret Cardiomyopathy

Introduction

While acquired cardiac disease is relatively common in older ferrets, congenital cardiac disease has yet to be documented in the species. Dilated cardiomyopathy is the most commonly reported form, although the hypertrophic form also occurs. Both primary (idiopathic) cardiomyopathy and cardiomyopathy secondary to another disease process, such as lymphosarcoma or intestinal bloat with myocardial ischemia, occur in ferrets. Cardiomyopathy usually progresses to congestive heart failure in this species.

Clinicians should become familiar with the clinical signs of cardiac disease in ferrets as well as methods available to evaluate cardiac health in older ferrets (e.g., as part of a preanesthesia evaluation). Multiple references that characterize echocardiography, electrocardiography, and radiography for both normal and sick ferrets are available. When performing a physical examination, practitioners should be aware that the normal heart rate for ferrets is 180 to 250 beats/min and the normal respiratory rate is 33 to 36 breaths/min. A pronounced sinus arrhythmia resulting in a dramatic decrease in heart rate during auscultation may also be normal in ferrets.

Laboratory Findings

Laboratory diagnostics should be pursued to confirm or exclude other important diseases that may occur concurrently with cardiomyopathy in middle-aged ferrets, such as adrenal neoplasia, lymphoma, dirofilariasis, Helicobacter infection, and insulinoma. Test results also provide a baseline for reference before initiating fluid and/or drug therapy in cardiac compromised patients. Normal reference ranges for ferrets are listed in Table 1; these values vary slightly depending on the gender and coloration of the individual ferret.

Complete Blood Count
Although no changes diagnostic of cardiomyopathy are found in the complete blood count, decreased leukocytes, total protein, hemoglobin, and hematocrit are present in many ferrets with cardiomyopathy.

Biochemical Profile

Abnormalities in the biochemical profile for ferrets with cardiomyopathy are similar to those in cats with cardiomyopathy.

Hypokalemia and elevated concentrations of creatinine and blood urea nitrogen have been documented in ferrets with cardiomyopathy.

Thrombosis and associated elevations in alkaline phosphatase, aspartate amino transferase, and creatinine kinase activities have not been reported in ferrets secondary to cardiomyopathy.

Feline Antigen Heartworm Test $

Negative.

The sensitivity and specificity of this test in ferrets are unproven; however, I have had several patients with positive test results that also were positive for heartworms at necropsy.

Thoracentesis or Abdominocentesis of Pleural Effusion or Ascites $

Fluid not normally obtained from the thorax or abdomen.

Although nonspecific, a transudate is usually present with cardiomyopathy.

Furosemide: 1–4 mg/kg PO, SC, IM, or IV q8–12h for diuresis. The endpoint of diuretic therapy is the relief of such clinical signs as pulmonary edema, pleural effusion, ascites, and dyspnea. $

Nitroglycerin 2% ointment: Initial adjunctive venodilator for cardiomyopathy and cardiogenic edema. Reduces pulmonary edema in the acute management of congestive heart failure. The ointment can be applied to a shaved inner thigh, the pinna, or any hairless region of skin at a dose of 1⁄16 to 1⁄8 inch/ferret q12–24h. $

Thoracentesis (if pleural effusion is present): Performed in a manner similar to that used in cats, except that the entry point should be farther caudal (i.e., at the ninth to 10th intercostal space) to avoid the more caudally located ferret heart. $

Alternative/Optional Treatments/Therapy

Treatment is based on the type of cardiomyopathy and can be initiated once the patient is stabilized. Combinations of an angiotensin-converting enzyme inhibitor with furosemide and other drugs based on the type of cardiomyopathy are generally used.

For long-term therapy, dosage is reduced to q6–8h once pulmonary edema has been reduced and then to the lowest effective oral dosage (q12–24h or even q48h)

Butorphanol (Torbugesic or Torbutrol, Fort Dodge Animal Health) $

0.05–0.4 mg/kg IM or SC as needed (usually <48 hours) for pain control and sedation

Digoxin $

0.005–0.01 mg/kg PO q12–24h for long-term therapy

Base dosage on lean body weight, usually 70% of body weight

Monitor serum concentrations 10–14 days after initiating therapy

Therapeutic concentrations of 1–2 ng/ml should be obtained 10–12 hours after oral administration

Anorexia and depression are early signs of toxicity

Draw blood samples for therapeutic monitoring if signs of toxicity are present

Draw blood samples for therapeutic monitoring 10–14 days after start of therapy and immediately before oral dosing for the trough concentration and 6–8 hours after oral administration for peak concentrations

Enalapril (Enacard, Merial) $

0.25–0.05 mg/kg PO q24–48h or q24h for long-term therapy

Propranolol $

0.2–2 mg/kg PO q8–12h for long-term therapy

Atenolol $

6.25 mg/ferret PO q24h for long-term therapy

Diltiazem $

1.5–7.5 mg/kg PO q12h for long-term therapy

Supportive Treatment

Fluid therapy as indicated based on assessment of hydration and pulmonary status. Vascular access may be obtained by an IV catheter placed in the cephalic or jugular vein or an intraosseous catheter and a 20- or 22-gauge spinal needle placed in the femoral, tibial, or humeral marrow cavity. $
—The recommended maintenance rate in ferrets is 70–100 ml/kg/24 hr; however, this rate may need to be substantially reduced (i.e., by 50% to 75%) depending on the patient’s hydration, perfusion, and pulmonary congestion status. Fluids may be given by slow drip or syringe pump over 24 hours.
—Recommended fluids include 2.5% dextrose in 0.45% sodium chloride solution or 5% dextrose in water (D5W).

Supplemental potassium may be given to hypokalemic patients in fluids or orally. Supplementation rates should follow guidelines used in cats and dogs.

Sedation and pain control may be indicated for ferrets that seem stressed or that refuse to allow a patent IV fluid line to be maintained. Low-dose butorphanol is an excellent sedative in ferrets

Many ill ferrets suffer from extreme hypothermia, and thermal support in the form of warmed fluids, forced heaters, or heating pads is indicated. The body temperature should be carefully monitored.

Patient Monitoring

Respiratory rate and work of breathing should be monitored until they normalize and lung crackles resolve.

Thoracic radiography is indicated to monitor alveolar infiltrates, which should clear within 24 to 72 hours of initiating therapy, and resolution of pulmonary effusion or edema.

Plasma blood urea nitrogen, creatinine, and electrolyte concentrations should be checked:
—The endpoint of diuretic therapy is relief of clinical signs and progressive increase in blood urea nitrogen and/or creatinine concentration.
—Hypokalemia and dehydration can result from excessive diuresis.

Serum digoxin concentrations should be monitored.

Echocardiography should be performed every 3 months to recheck fractional shortening and other cardiac dimensions.

Home Management

Exercise should be restricted, which may be difficult with ferrets.

A low-salt diet may be beneficial but difficult to institute because no such commercially available ferret diet is available.

Owners should be instructed to observe the animal for a recurrence of clinical signs, including but not limited to coughing, decreases in activity, lethargy, anorexia, and syncope.

Milestones/Recovery Time Frames

The initial response to therapeutic management should be monitored via observation of respiratory rate and effort as well as auscultation of lung sounds.

Other milestones and recovery time frames have not been reported; long-term clinical case management has not been reported retrospectively in ferrets.

Recommendations for recheck physical examinations and diagnostics are similar to those for management of congestive heart failure in other species:
—Electrocardiography, thoracic radiography, blood electrolytes, and renal indicators should be rechecked 7 to 10 days after initiating therapy.
—Ultrasonography to check cardiac size measurements, output, and contractility is indicated every 3 months.

Treatment Contraindications

Although anesthesia may be necessary for diagnostics and thoracentesis in ferrets with cardiomyopathy, any anesthetic event should be closely monitored.

Prednisone therapy may be necessary in patients with insulinoma but may rarely result in fluid and salt retention, making management of cardiac insufficiency more difficult.

Electrolytes should be carefully monitored in these patients; furosemide may result in hypokalemia, which is a contraindication for use of digoxin.

Digoxin should be used with caution in ferrets with renal disease. Digoxin is principally eliminated by the kidneys, and patients with renal insufficiency must have their levels carefully monitored. Ferrets with renal disease seldom have elevated creatinine values, although increased phosphorous and blood urea nitrogen concentrations are markers of renal disease in this species. Practitioners should be aware of how digoxin interacts with cimetidine, metoclopramide, and antacids before using these agents in ferrets with concurrent gastric ulcers and cardiac disease. Use of diuretics such as furosemide may predispose patients to digoxin toxicity. Use of steroids may deplete body potassium and thus may also predispose patients to digoxin toxicity.

Additional contraindications are listed for each drug separately under Alternative/Optional Treatments/Therapy.

Prognosis

Too few cases of cardiomyopathy in ferrets with long-term follow up have been reported to accurately assess the prognosis of ferrets with this disease. However, ferrets with more severe disease based on clinical signs and diagnostic testing seem to respond more favorably than dogs and cats with similar findings and medication regimens.

In contrast to the situation in cats, thromboembolic disease does not appear to be a common component of cardiovascular disease in ferrets. However, ferrets with petechia or ecchymoses carry a guarded prognosis and should be investigated for dirofilariasis and adrenal or other neoplasia.

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